Chopper



HJA. HOWELL- July 7, 1959 CHOPPER Filed March 19, 1958 1N VENTOR.

d. flea/1265. W L mm United States. Patent CHOPPER Hugh A. Howell, Berw'yn, 111., assignor to Oak Mfg. Co.,

. Cook County, 111., a corporation of Illinois Application March '19, 1958, Serial No. 722,438 1 Claim. (Cl. 200-90) This invention relates to a chopper, and more particularly to a chopper for handling minute amounts of electric power. While the chopper embodying the present invention may have a wide variety of application, it is particularly adapted for use in high impedance low voltage circuits.

It is well known that choppers are used in communication equipment for interrupting a DC. circuit in connection with the transmission of currents in resistive networks or through capacitors and through windings of transformers. In certain applications such as, for example, in airborne equipment, choppers are used in circuits haying impedances of the order of megohms with potentials'of .the order of microvolts.

The wave form of a chopper output in such equipment is of great importance, particularly in connection with auxiliary filters for providing a sine wave. Choppers available at the present time have been characterized by erratic wave form at the output of the chopper. In particular, choppers generally are troubled by the presence of an extremely sharp voltage spike occurring upon each make or break of contacts. This voltage spike, While of extremely short time duration has sufiicient amplitude to have a serious effect upon the chopper output.

While I am not certain of the exact cause for this objectionable behavior of present day choppers, I have definitely determined that a construction embodying the present invention provides complete insurance against the presence .of any-voltage spikes as pointed out above.

As is well known, all present choppers available on the market provide compressible insulator mountings for the chopper contacts. As a rule, the insulation used for mounting the contacts on a chopper include mica or other material bolted or riveted between rigid members of metal. I believe that such a type of mounting permits potential waves of high amplitude and short duration to be created during contact motion.

Such transients in what may be effectively considered as a dielectric between two minute capacitor plates results in a generation of electric current. Such transducer action is utilized in various piezo-electric and frictional electric devices. While the transducer action in present day choppers may be ineflicient, the low power level at which the choppers operate and the very high impedances which such choppers face render the transducer action of a chopper quite significant in relation to the chopper output.

In accordance with the present invention, I have eliminated all bolt or rivet type of mountings for chopper contacts and instead have provided a permanent type of insulating support utilizing a fused glass or ceramic contact mounting. While no attempt is made to provide a hermetic seal as is the case in such devices as vacuum tubes for example, the technique of mounting a metal conductor in a separate metal support by means of a fused glass or ceramic bead is well known.

In general, glass or ceramic of the type used in electrical devices not only provides a rigid mounting which 2,894,094 Patented July 7, 1959 ice withstands shock but appears to have a negligible output insofar as transducer action is concerned. This negligible output may be due in some measure to the nature of glass, apart from the generally rigid mechanical retention. In addition, the new mounting reduces capacitances between insulated parts. In any event, irrespective of underlying theory, the fact remains that I provide a chopper having an output substantially free of any voltage spikes caused by contact action by rigidly mounting all of the contacts both stationary and movable in a fused insulator such as glass or ceramic. For a fuller understanding of the invention, reference will now be made to the drawing wherein 'Fig. 1 is an elevation-with certain parts in section and certain parts broken away of a chopper embodying the present invention, the chopper having a housing around the same.

Fig. 2 is an elevation of the chopper minus the housing and minus the 'cnergiaing winding, Fig. 2 showing the chopper at right angles to Fig. 1.

Fig. 3 is a view of the chopper generally similar to Fig. l but showing the housing and winding removed.

Fig. 4 is a view looking down upon the chopper along the line 4-4 of Fig. 3.

Fig. 5 is a detail along line 5-5 of Fig. 4 illustrating a mountingfor the movable contact.

Fig. 6 is a view along line 6-6 of Fig. 4 illustrating the mounting for a stationary contact.

A chopper embodying-the present invention may have various structural features such as, for example, as illustrated in the drawing. In this chopper, permanent magnet 10 is rigidly clamped between ferro-magnetic frame side plates lljand 12. Permanent magnet 10 may be of any suitable material and preferably is of the so-called ceramic type now available on the market. Frame plates 11 and 12 are rigidly 'joined at the bottom by base plate 14 and are joined at the top by cross piece 15. Base plate 14 and cross piece 15 are preferably of non-magnetic material although if sufficiently thin they may be of ferro-magnetic material. The objective of base plate 14 and cross piece 15 is to provide a strong and rigid frame construction.

Side plates 11'- and '12 have upper portions 17 and 18 apertured and tapped to accommodate ferro-magnetic bolts 19 and 211 which function as adjustable pole pieces. Extending upwardly from side plates 11 and 12 as seen in Figs; 1 to 3' inclusive 'are'a pairof ferro-magnetic support arm'sZZand 23. Supportarms '22'and 2.3 are rigidlyand 'intimatl-y fsecuretlto extensions 17 and -18 and at' their free end support 'a combined armature and movable contact assembly generally indicated by 25.

As is illustrated in Fig. 5 in greater detail, the armature assembly consists of ferro-magnetic rod 26 permanently sealed in a glass bead 27 supported in metal sleeve 28 having mounting flange 29. Glass bead 27 is of suitable glass and has a high electrical resistance. The glass used is of the so-called hard glass type and is not of the soft or lead glass variety. The seal is of the socalled compression type seal available in the market and the components are so selected that good retention is secured over the desired temperature operating range for the chopper.

In general, choppers are required to operate under ambient temperature ranges from the order of about minus 50 C. to about C. This temperature range is exemplary and the exact range will be determined by specifications set up by the customer. Except for the fact that member 26 must be of ferro-magnetic material, a wide variety of metals and glass may be used. In fact, member 26 may be of suitable ferro-magnetic material having a thin coating of metal such as cooper which may be relied upon for actual sealing in the glass.

Inasmuch as such seals are readily available in the market, no detailed description of the material and co1nposition is necessary. It is, of course, necessary that member 26 have substantial spring thereto. Member 26 which consittutes an armature and movable contact extends down low enough so that it can operate, in a region between adjustable pole pieces 19 and 20. The free end portion of member 26 operates between two stationary contacts 31 and 32. These two stationary contacts are similar and one of these .is shown in detail in Fig. 6.

Each stationary contact comprises contact portion proper 34 and support portion 35. Support portion 35 is sealed in glass bead 36 which is sealed to and supported by metal sleeve 37 having flange 38. For both the stationary movable contacts, the .metal as fused to the glass is preferably round in :section, although .it may be in the .form of a flat strip. However, round wire is preferred since the technique ofihandling circularly symmetrical seals in glassis well known and highlydeueloped.

The exact nature of portion .35 .is unimportant so long as it is electrically conducting to some extent. Obviously, the magnetic properties of the stationary contact structure as a whole are unimportant. Since the chopper .generally works into circuits having high resistance, the elec trical conductivity of the metal sealed .in the glass 'is also unimportant. At most, the difference in resistance between various metals would be negligible insofar as the entire circuit is concerned.

For both the stationary and movable contacts, the

metal below the glass bead may be flattened to a strip.

In the case of movable contact 26, the strip form is desirable to promote flexing. In the case of stationary contact metal 35, flattened portion 40 simply makes it easier for soldering wires thereto.

In the case of the movable contact illustrated in Fig. 5, the metal sleeve around the glassbead may be soldered to bent tips of support arms 22 and 23. In the case of stationary contacts, metal sleeve 37.and flange 36 may be soldered to bracket 42. Bracket 42 is preferably of metal and may be supported in any suitable fashion such as, for example, by bolts 43 carried by the frame plates.

Wire connections are soldered "to the stationary and movable contact structures, the various wire connections going down to contact pins 45 carried by base 46. As a rule, contact pins are mounted in a metal base, each contact pin being secured in a ,glass bead in the base.

An energizing winding 50 is disposed around arms 22 and.23 and leads from the winding will also be connected to certain of the contact pins. The :entire construction may be housed in can 51 sealed .to base 46 to provide a generally hermeticrhousingjfor'thechopper.

As ,is well known,-alternating currentsimpressed upon winding 50 will cause annature 26 to vibrate between the 4 pole pieces formed by bolts 19 and 20. The free end of armature 26 will make contact alternately with sta tionary contact members 31 and 32.

It is not necessary that contact members 31 and 32 be of the same metal as portion 35 within the glass bead. In fact, it may be desirable to have the tips of fixed con tact members 31 and 32 of suitable noble metal such as platinum. It may also be desirable to have the portions of the movable contact which cooperate with the stationary contacts provided with fine contact heads of suitable metal, as platinum. In general, all the metal parts of the chopper may be suitably treated to prevent corrosion. As an example, all the metal parts may be gold plated. Instead of glass, such insulators as quartz or ceramic may be used. But in all cases, the contact member is attached to an insulator by fusion and the insulator is attached to its support by fusion.

What is claimed is:

A chopper comprising a pair ,of ferromagnetic members, a permanent magnet disposed between said mem bers, said members having opposed pole pieces, a long thin armature, means for supporting one end of said armature with the other end thereof free to vibrate between said pole pieces, said supporting means including a glob of glass into which the supported end of the armature is sealed, said supported end of said armature having a current lead therefrom, said supporting means including metal fused to the outside of saidglass glob, said chopper including a winding disposed around said armature and adapted to be supplied with alternating current for causing armature vibration, support members rigidly attached to said ferromagnetic members, each ferromagnetic member having one support member, a glass glob fused to each support member, each glass glob having sealed therein a metal contact member, the two metal contact members being disposed on opposite sides of the armature and being spaced from each other to function as stationary contacts for cooperation with the armature, said metal contact members having current leads connected thereto whereby when said chopper operates in a high impedance circuit, the separate but rigid glass supports for the three current carrying metal members render said chopper substantially free of potential spikes due to contact action.

References Cited in the 'file of this patent UNITED STATES PATENTS 2,121,607 Mcllvaine u June 21, 1938 2,450,499 Brown .Oct. ,5, 1948 2,677,027 Woods Apr. .27, 1954 2,698,366 Howell Dec. 28, 1-954 

